Cardan or universal joints are usually used when two torque-transmitting shafts whose aligned orientation is not always ensured are to be connected with each other.
The cardan joint then usually consists of two opposing joint yokes that are arranged twisted radially at an angle of 90° in relation to each other that each represents one end of the two shafts that are to be connected in an articulated manner. The cross member, which consists of two pin bearers offset against each other by 90°, is disposed between the joint yokes, the cross member being made of one piece so that the two pin bearers are rigidly connected with each other. The pin bearers are each supported, pivotally about their axes, in the two joint yokes.
With regard to the transmission of driving forces, the skilled person is regularly presented with the task of transmitting the rotational movement on the one hand, but, on the other, of eliminating vibrations and shocks if possible. Such interferences may, for example, be caused by vibrations from the drive unit. This problem is especially noticeable in automobile engineering, in particular in the area of the drive train, for example in the area of the cardan shaft where the vibrations between drive assembly and rear axle are transmitted without hindrance, and in the area of the steering line or in the steering column where, should conventional cardan joints be used, no insulation whatsoever is effected against low-frequency vibrations or shocks imposed by road bumps. Such interferences may, on the one hand, lead to damages in the drive train or the steering column and/or to adverse effects of an acoustic or mechanical nature for the driver.
For the purpose of uncoupling with regard to acoustics or vibration dynamics, in particular in the steering column, it is, for example, known to use a torsional elastic coupling with a so-called Hardy disk as an axially elastic coupling element or a loop disk. The Hardy disk is disposed, for example, in the steering column between the bottom cardan joint and a steering housing or steering gear or between the cardan joints. The Hardy disk, which is rigid in the direction of rotation, is formed such that it is soft in the direction of the steering column. As principle requires, the bending stiffness of the Hardy disk is relatively small. This causes a distortion of the Hardy disk with the bending moments from the cardan joint if the Hardy disk is arranged in series with the cardan joint, as is commonly the case. Since a Hardy disk alone (without a cardan joint), at least given appropriate life expectancies, is not suitable for connecting non-aligned shafts, the number of components is disadvantageously increased with the necessary arrangement in series with the cardan joint. Furthermore, the axial constructional space is increased thereby, and the usual compensation of the discontinuities by means of two cardanic joints arranged in anti-phase is disturbed by the additional Hardy disk since it works like an additional joint when placed in series.
The following is a discussion of relevant art pertaining to cardan joints. The discussion is provided only for understanding of the invention that follows. The summary is not an admission that any of the work described below is prior art to the claimed invention.
EP 0 563 940 B1 discloses a universal joint comprising two forks which are situated opposite one another with a 90° offset and which are each a part of each one of two shafts which are to be pivotally interconnected, or which are adapted each to be connected to each one of two shaft ends which are to be pivotally interconnected, and comprising two journal pairs which are offset by 90° from another and which form a journal cross and which are rotatable about their axis in the respective fork ends and, relative to the rotational axis of the shafts, are mounted for torque transmission, the two journal pairs being at least slightly pivotable relatively to one another in the plane formed by the journal cross, each journal being mounted in an anchor bracket and adjacent anchor brackets are interconnected by an elastic coupling element, whereby the elastic coupling element contains reinforcing inlays in loop form, which are disposed to be stationary and which each interconnect two adjacent anchor brackets and in that the reinforcing inlays in loop form are situated along the periphery of the universal joint in a loop plane which is perpendicular to the plane of the journal cross.
It must be regarded as a main disadvantage of the cross joint disclosed in EP 0 563 940 B1 that the two pairs of pins connect the own pins with each other integrally in different ways: The one pair uses a through bolt, the other pair is configured from two short pins that are connected with each other by means of an additional connecting portion. For this reason, a different production tool is required for the production of each pin or pair of pins, which makes the production of the cross joint extremely cost-intensive. The necessary connecting portion furthermore limits the axial and radial clearance of the joint. Furthermore, the need for axial constructional space can be optimized.
It is a further disadvantage that the cross joint disclosed in EP 0 563 940 B1 takes a lot of constructional effort and is thus very susceptible to malfunction. It must be considered a further disadvantage that the yokes must be designed small with regard to width and that thus, their yoke bearings must be designed to be bigger (more expensive) in order to transmit a sufficient torque given reasonable construction dimensions. If the flexible ring is damaged in the cross joint of EP 0 563 940 B1, a replacement ring must be supplied via the anchors. In addition, the cross joint is difficult to balance, especially in the case of shafts that rotate quickly.
EP 0 160 599 describes a flexible coupling device comprising first and second yokes which are intended to be fixed, respectively, to a drive member and a driven member, which each have arms arranged so that the arms of the first yoke are interposed with those of the second yoke, whereby to each yoke is fixed a support and these two supports are arranged opposite each other so that the facing surfaces of these supports are substantially perpendicular to the rotation axis of the device, in that an elastomeric linking element is fixed to these facing surfaces of the supports, and in that each support is fixed to the corresponding yoke by means of a spindle engaging in at least one opening in said support and in holes provided in the arms of said yoke.
GB 942,495 discloses a universal coupling for shafts comprising a flexible disc having coupling elements extending one on each side thereof, each for connection to one of the shafts to be coupled, the coupling elements being pivoted to the disc about axes at right angles and lying normally to the axis of the disc whereby, in use of the coupling, angular misalignment of the coupled shafts may be accommodated by pivoting of the coupling elements without flexure of the disc, the disc being composed wholly or mainly of plastic, rubber or the like resilient material which is unrestrained so as to be free to flex during use of the coupling.
It must be considered as a main disadvantage of the connection for shafts disclosed in GB 942,495 that the coupling elements are rotated with clearance towards the disk and with significant friction, the torsion clearance and the friction merely satisfying modest demands.
Therefore, what is needed is an improved universal joint of the type mentioned at the beginning with simple means in such a way that it is cheaper to produce from an economic standpoint, without the elastic coupling element having to convey significant bending moments.